Data Communications
AT&T Private Line Service OC-48
SERVICE DESCRIPTION
AND
INTERFACE SPECIFICATION
Issue 1.0
November 1998
©AT&T 1998 Printed in USA
ii
NOTICE
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Issue 1.0 (9/18/98)
OC-48 Service Description And Interface Specification
iii
Table of Contents
1.
INTRODUCTION........................................................................................................................... 1
1.1
1.2
1.3
2.
CONTENTS ................................................................................................................................. 1
ACRONYMS ................................................................................................................................ 1
RELATIONSHIP WITH OTHER AT&T TECHNICAL REFERENCES AND INDUSTRY STANDARDS .......... 3
SERVICE DESCRIPTION ............................................................................................................. 3
2.1
OC-48 INTER-OFFICE CHANNEL SERVICE .................................................................................... 3
2.1.1
Zero Mile IOC Service....................................................................................................... 4
2.2
NETWORK INTERFACE AND POINT-OF-INTERFACE........................................................................ 4
2.3
ACCESS ARCHITECTURE ............................................................................................................. 4
2.4
ACCESS ARRANGEMENTS ............................................................................................................ 6
2.4.1
Local Channel ................................................................................................................... 6
2.4.1.1
2.4.1.2
2.4.2
2.4.2.1
2.4.2.2
2.4.2.3
2.4.3
3.
Customer Provided Access................................................................................................. 7
Basic Customer Provided Access (BCPA) .................................................................................... 7
Common Interface Arrangement (CIA) ......................................................................................... 7
Baseline Access ........................................................................................................................... 7
Licensed Space Arrangement (LSA) ................................................................................... 7
SERVICE AVAILABILITY AND PERFORMANCE................................................................... 8
3.1
3.2
4.
Total Service - AT&T Provided Access ........................................................................................ 6
Coordinated Service - AT&T Coordinated Access ........................................................................ 6
SERVICE AVAILABILITY .............................................................................................................. 8
SERVICE PERFORMANCE PARAMETERS......................................................................................... 8
INTERFACE SPECIFICATIONS.................................................................................................. 9
4.1
PHYSICAL SPECIFICATIONS.......................................................................................................... 9
4.1.1
Network Interface .............................................................................................................. 9
4.1.2
Point of Interface............................................................................................................... 9
4.2
OPTICAL SIGNAL SPECIFICATIONS ............................................................................................... 9
4.2.1
Network Interface .............................................................................................................. 9
4.2.2
Point of Interface............................................................................................................... 9
4.3
LOGICAL SIGNAL SPECIFICATIONS ............................................................................................... 9
4.3.1
Section Overhead ............................................................................................................ 10
4.3.2
Line Overhead (for future use)......................................................................................... 10
4.3.2.1
4.3.3
5.
Automatic Protection Switching (APS)....................................................................................... 10
Path Overhead (for future use)......................................................................................... 10
SYNCHRONIZATION AND TIMING........................................................................................ 10
5.1
INTERNAL TIMING MODE .......................................................................................................... 10
5.2
EXTERNAL TIMING MODE ......................................................................................................... 11
5.3
TIMING VARIATION .................................................................................................................. 11
5.3.1
Jitter................................................................................................................................ 11
5.3.2
Wander............................................................................................................................ 11
6.
NETWORK ALARM AND STATUS CONDITIONS ................................................................. 12
7.
CUSTOMER PREMISES EQUIPMENT CHARACTERISTICS .............................................. 12
7.1
7.2
7.3
CPE REQUIREMENTS ................................................................................................................ 12
LOOPBACK ............................................................................................................................... 12
AUTOMATIC PROTECTION SWITCHING ....................................................................................... 13
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OC-48 Service Description And Interface Specification
iv
8.
TESTING AND MAINTENANCE............................................................................................... 13
9.
REFERENCES.............................................................................................................................. 14
Figure 1 - Typical Point-to-point OC-48 Circuit ....................................................................................... 4
Figure 2 - OC-48 LC Circuit and Access Network Components................................................................ 5
Figure 3 - APLS OC-48 Access Connections ............................................................................................ 6
Figure 4 - External Timing Mode ........................................................................................................... 11
Figure 5 - Optical Loopback at NI .......................................................................................................... 12
Table 1. Optical Power Requirements at the NI......................................................................................... 5
Table 2. Optical Power Requirements at the POI ...................................................................................... 5
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OC-48 Service Description And Interface Specification
1
1. INTRODUCTION
This Technical Reference provides Network Interface (NI) and Point of Interface (POI) Specifications for
the AT&T Private Line OC-48 (Optical Carrier Level 48) Service. The document includes a description
of the service, technical parameters, physical interface requirements, logical interface requirements, and
other necessary criteria for connecting Customer Premises Equipment (CPE) and/or access to AT&T OC48 circuits to obtain the performance characteristics identified in Section 3.
In conformance with the approach used in Industry Standards, this document uses "shall" to signify a
mandatory requirement, and the word "should" to indicate recommended or advisory criteria.
1.1 Contents
The document consists of 8 sections that cover the following subjects:
Section 1. Introduction
Section 2. Service Description
Section 3. Service Availability and Performance
Section 4. Interface Specifications
Section 5. Synchronization and Timing
Section 6. Network Alarm and Status Conditions
Section 7. Customer Premises Equipment Characteristics
Section 8. Testing and Maintenance
1.2 Acronyms
ABMSC
ADM
AIS
AIS-L
AIS-P
ANSI
APLS
APS
BCPA
BCRC
BIP
BITS
CAP
CO
CP
CPA
CPE
dBm
CV-P
DCC
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AT&T Bandwidth Management Service Center
Add/Drop Multiplexer
Alarm Indication Signal
Alarm Indication Signal Line
Alarm Indication Signal Path
American National Standards Institute
AT&T Private Line Service
Automatic Protection Switching
Baseline Customer Provided Access
Business Continuity Recovery Center
Bit Interleave Parity
Building Integrated Timing Source
Competitive Access Provider
Central Office
Customer Premise
Customer Provided Access
Customer Premise Equipment
Decibels (referenced to milliwatt)
Code Violation Path
Data Communications Channel
OC-48 Service Description And Interface Specification
2
DS1
DS3
EFS
%EFS
EIA
ES-P
FC
FCC
IOC
IR
ISO
ITU-T
LC
LEC
LGX
LOF
LOP
LOP-P
LOS
LTE
Mbps
NE
NI
nm
OC-12
OC-3
OC-48
POI
POP
PTE
RDI-L
REI-L
RFI-P
SC
SCPA
SES-P
SMF
SONET
SR
ST
STS
STS-1
STS-12
STS-12c
STS-3
STS-3c
STS-48
STS-48c
STS-N
STS-Nc
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Digital Signal Level 1
Digital Signal Level 3
Error Free Seconds
Percent Error Free Seconds
Electrical Institute of America
Error Second Path
Optical Connector Type Ferrule Connector
Federal Communications Commission
Inter-Office Channel
Intermediate Reach
International Standards Organization
International Telecommunications Union – Telecommunications
Standardization Sector
Local Channel
Local Exchange Carrier
Light Guide Cross-connect
Loss of Frame
Loss of Pointer
Loss of Pointer Path
Loss of Signal
Line Terminating Equipment
Megabits per second
Network Element
Network Interface
nano-meter
Optical Carrier Level 12
Optical Carrier Level 3
Optical Carrier Level 48
Point of Interface
Point of Presence
Path Terminating Equipment
Remote Defect Indication Line
Remote Error Indicator Line
Remote Failure Indicator Path
Optical Connector Type Square Connector
Shared Customer Provided Access
Severely Error Seconds Path
Single-Mode dispersion-unshifted Fiber
Synchronous Optical NETwork
Short Reach
Optical Connector Type Straight Tip
Synchronous Transport Signal
Synchronous Transport Signal Level 1
Synchronous Transport Signal Level 12
Synchronous Transport Signal Level 12 Concatenated
Synchronous Transport Signal Level 3
Synchronous Transport Signal Level 3 Concatenated
Synchronous Transport Signal Level 48
Synchronous Transport Signal Level 48 Concatenated
Synchronous Transport Signal Level N
Synchronous Transport Signal Level N Concatenated
OC-48 Service Description And Interface Specification
3
SWC
T1
T3
TCPA
TR
VT1.5
Serving Wiring Center
DS1 Electrical Interface and Carrier
DS3 Electrical Interface and Carrier
Turnkey Customer Provided Access
Technical Reference
Virtual Tributary containing a DS1
1.3 Relationship With Other AT&T Technical References And Industry
Standards
Interface specifications pertaining to ACCUNET T45 Service can be found in Technical Reference (TR)
54014 and its addenda[1]. Interface specifications pertaining to ACCUNET T1.5 Service can be found in
TR 62411[2]. Access specifications for ACCUNET T1.5 and T45 can be found in TR 62415[3].
Information about the optical interface and payload mappings can be found in (with their supporting
references): AT&T TR 54018 OC-3 Optical Interface Specifications[4], AT&T TR 54077 OC-12 Service
Description and Interface Specification[5], ANSI T1.101-1994 – Synchronous Interface Standards[6], ANSI
T1.105.01-1994 Telecommunications – Synchronous Optical Network (SONET) – Automatic Protection
Switching[7], ANSI T1.105.02-1995 Telecommunications – Synchronous Optical Network (SONET) –
Payload Mappings[8], ANSI T1.105.03-1995 Telecommunications – Synchronous Optical Network
(SONET) – Jitter at Network Interfaces[9], ANSI T1.105.03a-1995 Telecommunications – Synchronous
Optical Network (SONET) – Jitter at Network Interfaces – DS1 Supplement[10], and ANSI T1.105.03b1997 Telecommunications – Synchronous Optical Communication (SONET) – Jitter at Network
Interfaces – DS3 Wander Supplement[11], ANSI T1.105.04-1995 Telecommunications – Synchronous
Optical Network (SONET) – Data Communication Channel Protocols and Architectures [12], ANSI
T1.105.06-1995 Synchronous Optical Network (SONET) – Physical Layer Specifications[13], ANSI
T1.105.09-1995 Telecommunications – Synchronous Optical Network (SONET) - Timing and
Synchronization[14], ANSI T1.107-1995 Telecommunications - Digital Hierarchy - Formats
Specifications[15], ANSI T1.231-1997 – Digital Hierarchy – Layer 1 In-service Digital Transmission
Performance Monitoring[16], ANSI T1.514-1995 Network Performance Parameters and Objectives for
Dedicated Digital Services – SONET Bit Rates[17], Bellcore Synchronous Optical Network (SONET)
Transport Systems Common Generic Criteria (GR-253-CORE)[18], Bellcore Transport Systems Generic
Requirements (TSGR): Common Requirements (GR-499-CORE)[19], Bellcore Clocks for the Synchronized
Network: Common Generic Criteria (GR-1244-CORE)[20], Bellcore SONET Private Line Service Interface
Generic Criteria for End Users (GR-1365 CORE)[21], ATM Forum af-phy-0046.000 “2488.32 Mbps
Physical Layer Specification,” January 1996[22].
AT&T intends to continue to review the emerging SONET (Synchronous Optical NETwork) standards as
they are defined and adopt them as appropriate.
2. SERVICE DESCRIPTION
2.1 OC-48 Inter-Office Channel Service
The AT&T Private Line Service (APLS) OC-48 Inter-Office Channel (IOC) Service is a service that
provides dedicated point-to-point 2488.32 Megabits per second (Mbps), or 2.48 Gbps, line rate digital
service for STS-48/48c (Synchronous Transport Signal Level 48/48 concatenated) signals. A point-topoint service is defined as a two-way service where traffic originates (or terminates) in one location and
terminates (or originates) in the other. Besides STS-48c signals, the OC-48 IOC may be comprised of
STS-1 (Synchronous Transport Signal Level 1), and/or STS-3c (Synchronous Transport Signal Level 3
concatenated), and/or STS-12c (Synchronous Transport Signal Level 12 concatenated) tributary signals as
Issue 1.0 (9/18/98)
OC-48 Service Description And Interface Specification
4
required per customer application. The differences between the line rates and effective customer payloads
are due to bits reserved for SONET overhead signaling. More details about SONET format standards are
given in Section 4 “Interface Specifications”. OC-48 service features optical interfaces at the NI and the
POI. Figure 1 below illustrates a typical point-to-point OC-48 circuit with significant components and
points of demarcation.
CPE
Access
NI
IOC
POI
CPE
Access
POI
NI
Note – All NI and POI interfaces are Optical.
Figure 1 - Typical Point-to-point OC-48 Circuit
2.1.1 Zero Mile IOC Service
Zero Mile IOC Service is a special configuration that supports OC-48 connectivity in the same office, i.e.
access-to-access.
2.2 Network Interface and Point-Of-Interface
Per Federal Communications Commission (FCC) Tariff 9, the definition of the NI is the point of
demarcation on the end user’s premises at which the access supplier’s responsibility for the provision of
access ends. The POI is defined as the point of demarcation between AT&T and an access supplier. The
POI located in an AT&T Central Office (CO) establishes the service demarcation between access and the
IOC.
The NI and POI for OC-48 shall be optical. This signal shall be comprised of STS-1 and/or STS-3c,
and/or STS-12c, or STS-48/48c (as required by customer applications) formatted tributaries per Bellcore
GR-253-CORE[18] Section 3.2, ANSI T1.105.02[8]. The signal at the NI and POI shall conform to the
SONET standards per GR-253-CORE[18] Section 3, ANSI T1.105.02[8]. Path overhead shall only
terminate at the CPE or equivalent end-point of the SONET channel. 2-fiber and 4-fiber interconnections
are supported for both NI and POI. The 4-fiber POI interconnection shall be used to support SONET APS
(Automatic Protection Switching)1.
2.3 Access Architecture
Figure 2 illustrates a typical access connection. The CPE is connected to the OC-48 service via the NI.
The NI should allow test access to all of the fiber pairs interconnecting the CPE with the access supplier’s
OC-48 Line Terminating Equipment (LTE). The NI is typically located on customer premises. The
Network Interface for OC-48 Local Channel (LC) is defined as an Optical Fiber Connection Panel.
1
This APS function shall be performed by customer premise equipment or access vendor (AV) equipment
at NI, and only by AV equipment w/ Local Channel access at POI (see Sec. 2.4).
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OC-48 Service Description And Interface Specification
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ACCESS SYSTEM
Supplier
Management Center
CUSTOMER
PREMISES
AT&T POP
Serving Wire Center (SWC)
SWC
NI
Loop
N
o
d
e
IOF
N
o
d
e
POI
Feed
POI
Figure 2 - OC-48 LC Circuit and Access Network Components
The 2488.32 Mbps signal at the NI shall be Optical in both directions. The optical power levels required
at the NI should be compliant with standards for Short Reach (SR) optics per GR-253-CORE[18] Section
4.1 and 4.2 and ANSI T1.105.06[25] and are given in Table 1 in dBm (decibels milliwatt reference). Also,
the Customer Installation shall meet the loss requirements as specified in GR-253-CORE[18] section 4.2.
The CPE will determine the fiber type (single mode or multi-mode) to connect the CPE to the NI Optical
Fiber Connection Panel. Table 1 shows the AT&T required levels. The NI Optical Fiber Connection
Panel supports optical connector options as required by the customer application (i.e., SC, FC, ST, etc.).
The NI configuration supports 2 fiber (one pair) duplex unprotected operation, or 4 fiber (two pairs)
operation, that can be either duplex unprotected2 or 1+13 SONET automatic protection switching (APS)
operation based on customer application needs, and the Access Provider infrastructure capabilities1.
Table 1. Optical Power Requirements at the NI
Receive to CPE
Pmax: -3 dBm
Pmin : -18 dBm
Transmit from CPE
Pmax: -3 dBm
Pmin : -10 dBm
The OC-48 POI is implemented via an AT&T-owned Light Guide Cross-Connect (LGX) shelf with ST
bulkhead connectors. Single mode fiber to AT&T assigned jacks on the rear of the LGX POI shelf shall
be used. POI interconnections are implemented over 2 fibers (one pair) and 4 fibers (two pairs)
configuration. The 4-fiber POI interconnection shall be used to support SONET APS (Automatic
Protection Switching)1 with Local Channel access only (see Sec. 2.4.1).
The 2488.32 Mbps signal at the POI shall be Optical in both directions. Signal power levels at the POI
are to be within the following range:
Table 2. Optical Power Requirements at the POI
Receive to AT&T
Pmax: -3 dBm
Pmin : -14 dBm
2
3
Transmit from AT&T
Pmax: -3 dBm
Pmin : -14 dBm
For 4-fiber DWDM applications at the NI only, but not at the POI.
The term 1+1 protection means one active service line plus one protection line.
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OC-48 Service Description And Interface Specification
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Note: AT&T expects that under most circumstances these levels can be achieved using SR capable
equipment with a 4 dB fiber loss budget from access vendor equipment to POI, and a 4 dB fiber loss
budget from AT&T equipment to POI.
Figure 3 illustrates the OC-48 connections at the NI and POI.
Customer
Premises
AT&T CO
CPE
(PTE)
OC48
Netw
ork
Equi
pmen
t
Access
Network
(where supported)
(where supported)
LGX
CPE – Customer Premise Equipment
PTE – Path Terminating Equipment
LGX – Light Guide Cross-connect
NI
POI
Optical Fiber Connection Panel
Figure 3 - APLS OC-48 Access Connections
The customer shall provide the STS-1, STS-3c, STS-12c, or STS-48c mapping into an OC-48 to AT&T,
and shall conform to the permitted combinations per SONET OC-48 format specification in GR-253CORE[18], Sec. 3.
2.4 Access Arrangements
Customers may provide their own access to OC-48 Service, or may acquire access through AT&T or a
third party.
2.4.1 Local Channel
Note: This is the ONLY access arrangement that can be used to support 4-fiber interface at the POI.
2.4.1.1 Total Service - AT&T Provided Access
The customer may purchase an OC-48 in Total Service arrangement from AT&T, that provides access
and customer premises to customer premises connectivity. Under this access arrangement, AT&T is the
customer of record for the access circuit used to provide customer access to the AT&T POP. AT&T is
responsible for maintenance.
2.4.1.2 Coordinated Service - AT&T Coordinated Access
For this access arrangement, access is coordinated by AT&T with the access provider. The access is
ordered at the time the customer initiates a Service Order. When providing coordinated access, AT&T
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OC-48 Service Description And Interface Specification
7
assumes responsibility to work with the access provider for the following functions: Design, Ordering,
Installation coordination, Pre-service testing and service turn-up, Trouble sectionalization and Restoration
coordination. Under this access arrangement, the end-customer is the customer of record for the access
circuit used to provide customer access to AT&T.
2.4.2 Customer Provided Access
Note: This access arrangement CANNOT be used to support 4-fiber interface at the POI.
2.4.2.1 Basic Customer Provided Access (BCPA)
Under Basic Customer Provided Access (BCPA), the access facilities are furnished and owned by the
customer from the Customer Installation (CI) at CP to the servicing AT&T CO. The serving AT&T CO
must be a designated OC-48 Point Of Presence (POP). The customer also has terminal equipment located
in the AT&T POP (i.e., the end-user is the customer of record). The customer pays for space, power,
light, etc.
Under this arrangement, the customer has total responsibility for the engineering, installation, operation,
and maintenance of the BCPA facility terminating at the AT&T POP. AT&T provides the installation,
maintenance, and testing support required to interconnect the BCPA to the OC-48 POI.
2.4.2.2 Common Interface Arrangement (CIA)
Under Common Interface Arrangement (CIA)4, the access facilities are acquired by the customer from the
Customer Installation (CI) at CP to the serving AT&T CO. Similarly, the serving AT&T CO must be a
designated OC-48 Point Of Presence (POP). The access is provided by licensed/regulated
telecommunication providers (i.e., the LEC or AAV is the customer of record). Access Provider has
terminal equipment in the AT&T POP, and the access provider pays for space, power, light, etc. The
access provider can provide access for multiple, different customer circuits via such an arrangement.
Under this arrangement, the customer, together with the access provider, has total responsibility for the
engineering, installation, operation, and maintenance of the CIA facility terminating at the AT&T POP.
AT&T provides the installation, maintenance, and testing support required to interconnect the CIA
facility to the OC-48 POI.
2.4.2.3 Baseline Access
Under Baseline Access arrangement, the customer purchases their access directly from the access
provider, and has it installed. Baseline is the same as CIA (see above), as customer purchases the access
circuit from an access provider that in turn provides the customer access to AT&T POP via an CIA
arrangement.
2.4.3 Licensed Space Arrangement (LSA)
Note: This access arrangement CANNOT be used to support 4-fiber interface at the POI.
This access arrangement allows the customer to lease space in the AT&T servicing CO for customer
owned equipment, that is interconnected to AT&T equipment in that CO. Under this access arrangement,
the Customer Installation (CI) is in the same office as the POI and are interconnected with intra-office
optical fiber facility.
4
This used to be called SCPA (Shared Customer Provided Access).
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OC-48 Service Description And Interface Specification
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3. SERVICE AVAILABILITY AND PERFORMANCE
3.1 Service Availability
Availability is a measure of the time during which the circuit is available for useful transmission. This
measurement is the complement of unavailability or Outage (%Availability = 100 - %Outage). An outage
begins when the customer releases a circuit to AT&T for repair and ends when AT&T returns the circuit
to the customer.
3.2 Service Performance Parameters
The error performance parameters Code Violations, Error Seconds, and Severely Error Seconds have been
defined for SONET Section layer, Line layer, and STS Path layer5 in GR-253-CORE[18] section 6.2.2,
ANSI T1.231[16], ANSI T1.514[17], and ANSI T1.105.04[12]. They are reproduced here for reference, and
are described as measurements of corresponding events over a certain time interval. Note that various
equipment vendors and communications service providers may have implemented these definitions
differently.
•
•
•
•
Code Violations (CVs) – The CV parameter is a count of Bit Interleave Parity (BIP) errors detected at
the incoming SONET signal: CV-S for the Section layer, CV-L for the Line layer, and CV-P for the
STS Path layer. They are collected using the overhead bytes (e.g., B1, B2, B3) in various SONET
Overhead.
Error Seconds (ESs) – The ES parameter is a count of one second intervals during which at least one
BIP error occurred, or one second intervals during which (at any point during the second) a defect or
failure was detected at the incoming SONET signal. They are ES-S for the Section layer, ES-L for
the Line layer, and ES-P for the STS Path layer. Examples of defects are LOS, SEF, AIS-L, AIS-P,
and LOP-P.
Severely Error Seconds (SESs) – The SES parameter is a count of one second intervals during which
K or more BIP error occurred, or one second intervals during which (at any point during the second)
a defect or failure was detected at the incoming SONET signal. They are SES-S for the Section layer,
SES-L for the Line layer, and SES-P for the STS Path layer. The values of “K” have changed several
times in the past and are currently set in GR-253-CORE[18] as follows: 2,392 for SES-S, 2,459 for
SES-L, and 2,400 for SES-P. Examples of defects are LOS, SEF, AIS-L, AIS-P, and LOP-P.
Percent of Error Free Seconds (%EFS) – Percent EFS is defined as the ratio of one-second intervals
not containing any bit errors to the total number of seconds in an observation period, which is usually
24 hours. The percent EFS calculation applies only to time intervals over which the circuit is
available.
It is noted that both near-end and far-end parameters are defined for the Line layer and STS Path layer
parameters: CV-L, CV-LFE, ES-L, ES-LFE, SES-L, SES-LFE, CV-P, CV-PFE, ES-P, ES-PFE, SES-P,
and SES-PFE. Far-end Line layer performance is conveyed back to the near-end LTE (Line Terminating
Equipment) via the K2 byte (RDI-L) and the M0 or M1 byte (REI-L). And far-end STS Path layer
performance is conveyed back to the near-end STS PTE (Path Terminating Equipment) via bits 1 through
4 (REI-P) and 5 through 7 (RDI-P) of the G1 byte. 6 The far-end performance parameters are defined with
these remote indication signals.
5
Only the Section layer error performance parameter may be monitored by AT&T initially. These
parameters for other layers may be monitored in the future.
6
It is noted that REI-L, REI-P and RDI-P may not be fully supported with the SONET Multiplex Function
(SMF) service option.
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OC-48 Service Description And Interface Specification
9
4. INTERFACE SPECIFICATIONS
The signal at the NI and POI shall conform to the relevant SONET standards (see Sec. 1.3) for OC-48
signals as cited in the following sections. The NI and POI are specified in terms of three layers: Physical,
Optical, and Logical. The logical level is further broken down into Section, Line, and Path layers.7
4.1 Physical Specifications
All physical connectivity to the POI shall be via dispersion-unshifted Single-Mode Fiber (SMF)8. Physical
connectivity to the NI may be over one or two fiber pairs. These fiber connections shall conform to GR1365[21], Section 3.4. Two pairs of fiber (one pair for service and one pair for protection) are used to
support protected switching operation (see Sec. 2.2).
4.1.1 Network Interface
The physical interface at the NI shall be an optical fiber connector panel, that supports optical connector
options as required by the customer application (e.g., SC, FC, ST, etc.). The connector panel will allow
ease of CPE connection and the ability to create a manual loopback for testing.
4.1.2 Point of Interface
The physical interface at the POI shall be the AT&T LGX. The pair assignment on the LGX will be
administered by AT&T. ST connectors shall be used for the LGX at the POI9.
The access supplier will have responsibility and ownership of all access facilities up to the LGX POI10.
Access supplier entry will be allowed for installation and maintenance activities up to the POI. AT&T
will provide space, environment and power (for equipment required in the AT&T building) for the access
supplier to deliver access.
4.2 Optical Signal Specifications
Optical signals at the NI & POI shall conform to the OC-48 signal characteristics described in GR-253CORE[18] Sec. 4.1 and 4.2 and ANSI T1.105.06[13] with sources at the nominal 1310 nano-meter (nm)
wavelength.
4.2.1 Network Interface
CPE shall follow the optical interface specifications for the application category relevant to the CPE
vendor requirements. The customer shall provide a system compatible with the access facility. CPE
should follow the optical interface specifications for the application category as given in GR-1365[21].
4.2.2 Point of Interface
The AT&T equipment at the POI, as one point on the optical path between transmitter (Point S) and
receiver (Point R), meet the optical category specified as OC-48 SR MLM in GR-253-CORE[18] Sec 4.2
and ANSI T1.105.06[13].
4.3 Logical Signal Specifications
The logical signal (Synchronous Transport Signal Level N (STS-N/Nc)) contains the customer payload
along with the section, line, and path overhead required by the SONET standard. The STS-N/Nc signal
shall conform to the STS-1 and/or STS-3c and/or STS-12c or STS-48/48c formats as defined in GR-2537
Initially, only the Section layer interface will be observed by AT&T.
Dispersion-shifted SMF is recommended ONLY for LR-3 (Long Reach-3) application.
9
A different connector may be used by the new LGX at the POI in the future.
10
The access supplier here refers to the access vendor in all access arrangements except LSA. (see Sec.
2.4)
8
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OC-48 Service Description And Interface Specification
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CORE[18] Section 3 and ANSI T1.105.02[8]. The customer shall notify AT&T of the signaling format and
tributary configuration. The customer shall keep a valid signal on the circuit in order to maintain
performance monitoring. The CPE or network equipment shall not be turned off without notifying
AT&T.
4.3.1 Section Overhead
The STS-N shall provide all Section overhead functions with the possible exception of the Section Data
Communications Channel (DCC) (bytes D1-D3), Section Orderwire (byte E1), and Section User Channel
(byte F1). To manage network integrity and sustain service quality, section DCC capabilities through the
AT&T network and access segment is not supported. Therefore, any information contained in the bytes
reserved for Section DCC (D1-D3), Section Orderwire (E1), and Section User Channel (F1) may not be
transported end-to-end (NI-to-NI). This is consistent with SONET standards for section overhead.
4.3.2 Line Overhead (for future use)
The STS-N shall provide all Line overhead functions with the possible exception of Line DCC (bytes D4D12), Synch Status Messaging (byte S1), and Line Orderwire (byte E2). To manage network integrity
and sustain service quality, line DCC capabilities through the AT&T network is not supported. Line
overhead is terminated at or before the AT&T network, therefore, any information contained in the bytes
reserved for Line DCC (D4-D12) and Line Orderwire (E2) will not be transported end-to-end (NI-to-NI).
This is consistent with the SONET standard for Line overhead. At the time of this publication, AT&T
does not support any functionality based on the use of growth bytes. Information contained in these bytes
may not be transported.
4.3.2.1 Automatic Protection Switching (APS)
GR-253-CORE[18] Section 5.3 and ANSI T1.105.01[7] specify criteria for implementing Automatic
Protection Switching (APS). When APS function is supported via the 4-fiber interface (see Sec. 2.2), the
STS-N shall conform to linear 1+1, unidirectional, non-revertive protection switching. The term
“unidirectional” means that only the impaired direction of service will be restored.
4.3.3 Path Overhead (for future use)
The STS-N or STS-Nc shall provide all Path overhead functions with the possible exception of Path User
Channel (byte F2), and Growth Channels (bytes Z3 and Z4). Use of bytes F2 and H4 is optional, but must
be in accordance with ANSI T1.105.02[25] and GR-253-CORE[18]. As per ANSI T1.105, bytes Z3 and Z4
are reserved for future use11. At the time of this publication, AT&T does not support any functionality
based on the use of these growth channels. The service shall be STS-1 and/or STS-3c and/or STS-12c or
STS-48/48c end-to-end. Path status and parity bytes may be monitored for performance information.
5. SYNCHRONIZATION AND TIMING
All CPE and network equipment providing AT&T OC-48 service shall conform to timing and
synchronization specifications described in ANSI T1.105.09[14], ANSI T1.101[6], and GR-1244[20]. The
access supplier equipment should be able to receive timing from a co-located external reference clock of
Stratum 3 or higher accuracy traceable to a Stratum 1 source. CPE may be timed to an internal clock or a
co-located external reference clock of Stratum 3 or higher accuracy traceable to a Stratum 1 source.
5.1 Internal Timing Mode
CPE timed in internal timing mode draws its synchronization from its own timing source. This source
shall not exceed the maximum free run deviation of + 20ppm. In this case, CPE at one of the two ends
would need to be designated as the master.
11
Byte Z4 may be used for AT&T network maintenance in the future.
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5.2 External Timing Mode
CPE timed in external timing mode draws its synchronization from an independent timing source. This
source shall be Stratum 3 or better and traceable to a Stratum 1 source. This configuration is shown in
Figure 4. In this case, CPE at one of the two ends would need to be designated as the master as well.
BITS
(Stratum 3
or better)
Customer
Premises
NE
CPE
OC-48
T
Figure 4 - External Timing Mode
5.3 Timing Variation
5.3.1 Jitter
Timing jitter is the short term (> 10 Hz) variation in the significant instances of a digital signal as
compared to an ideal clock. GR-253-CORE[18] section 5.6, ANSI T1.105.03[9], and ANSI T1.105.03a[10]
contains equipment jitter specifications (i.e. jitter transfer, jitter tolerance, and jitter generation) that are to
be used to engineer CPE to the Network Interface Jitter Specification. In particular, the Network Interface
Jitter Specification for OC-48 service is the following (per GR-253-CORE[18] Sec. 5.6):
Timing jitter at network interface shall not exceed 1.5 Unit Intervals peaek-to-peak (UIpp) when
measured over a 60-second interval with a band pass filter having a lower cutoff frequency of 5000Hz
(and a roll-off of 20dB/decade) and an upper cutoff frequency of at least 20MHz.
Timing jitter at network interface shall not exceed 0.15 Unit Intervals peaek-to-peak (UIpp) when
measured over a 60-second interval with a band pass filter having a lower cutoff frequency of 1000kHz
(and a roll-off of 20dB/decade) and an upper cutoff frequency of at least 20MHz.
CPE designs shall be engineered to have a tolerance specification which is better than the requirements
represented above to ensure problem free operation.
5.3.2 Wander
Timing wander is the long-term (< 10 Hz) variation in the significant instances of a digital signal as
compared to an ideal clock. GR-253-CORE[18] section 5.4.4.3.2, GR-1244[20] sections 4.3 and 5.4, ANSI
T1.105.09[14], and ANSI T1.105.03b[11] contains equipment wander specifications (i.e. wander transfer,
wander tolerance, and wander generation) that are to be used to engineer CPE to the Network Interface
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Specification. CPE designs shall be engineered to have a wander specification which is better than the
requirements represented by the standard to ensure problem free operation.
6. NETWORK ALARM AND STATUS CONDITIONS
AT&T will detect LOS and monitor the SONET Section layer overhead (see Sec. 4.3.1). And the access
network equipment shall monitor SONET signals to detect LOS.
7. CUSTOMER PREMISES EQUIPMENT CHARACTERISTICS
7.1 CPE Requirements
CPE shall generate alarms as described in GR-253-CORE[18] Section 6. CPE shall monitor SONET
signals to detect LOS, LOF, and LOP. And the CPE shall transmit maintenance signals when failure
states are detected in the network. Maintenance signals include AIS-L, RDI-L, RFI-L, AIS-P, RDI-P, and
RFI-P. For any unused STS-12c, STS-3c and/or STS-1 channels, the CPE shall transmit a valid idle code
and set the path label to unequipped.
7.2 Loopback
Customer Premises
CPE
Optical
Loopbacks
For
Testing
NI
Optical Fiber Connection Panel
Figure 5 - Optical Loopback at NI
To conduct circuit testing and fault sectionalization of the two-way OC-48 circuit, an optical loopback on
the CPE side of the NI toward the network shall be provided as shown in Figure 5. To aid in the
sectionalization, an optical loopback on the CPE side of the NI toward the CPE (facility loopback) and one
toward the network (terminal loopback) should be provided as shown in Figure 5. AT&T will coordinate
with the customer when loopbacks are required and will enlist the customer’s support in establishing
loopbacks at the NI. This optical loopback is not recommended when the CPEs use internal timing.
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7.3 Automatic Protection Switching
Protection switching is described in GR-253-CORE[18] and ANSI T1.105[13], Section 13. When APS is
provided, all CPE should be designed to tolerate an upstream protection-switching event without declaring
a failure.
8. TESTING AND MAINTENANCE
The OC-48 Service will be managed as an 2488.32 Mbps circuit transporting STS-1 and/or STS-3c and/or
STS-12c, or STS-48c tributaries as specified. Testing and maintenance may require the customer to
relinquish the full circuit of 2488.32 Mbps.
A point of contact for testing and maintenance issues will be provided by AT&T at the time of service
installation. AT&T can perform testing and repair most efficiently when a complete and accurate
description of the trouble is provided by the customer. Information such as date, time, and nature of the
problem should be provided in reporting trouble.
In addition, the customers should be acquainted with the basic equipment layouts, visual indicators on
CPE, and be knowledgeable in fundamental maintenance techniques. For customer provided access
arrangements (i.e., BCPA, CIA, and Baseline), the customer should also know how to work with the
access provider for the maintenance (including trouble shooting) of the access facilities. When problems
are encountered by the customer, it is essential that the CPE (and access facilities that are non-AT&T
maintained) be checked for proper operation before reporting the trouble. Diagnostics capabilities of the
CPE, such as loopbacks (shown in Figure 5), can also be useful in trouble isolation. This action will
eliminate unnecessary dispatches of repair personnel by AT&T. For such dispatches; the customer may be
required to pay a “maintenance or service charge” if the problem is isolated to the customer’s segment of
the circuit.
Once the customer reports a trouble to AT&T, the customer should provide a contact for assistance at CP
during trouble shooting and any necessary repair, as well as for verification of trouble resolution before
the circuit is put back in normal service. AT&T will provide periodic status report of the customer
reported trouble.
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9. REFERENCES
1.
ACCUNET T45 and T45R Service Description and Interface Specifications, AT&T Technical
Reference 54014, May 1992 and addendum 1 November 1992
2.
ACCUNET T1.5 Service Description and Interface Specifications, AT&T Technical Reference
62411, December 1990
3.
Access Specification For High Capacity (DS1/DS3) Dedicated Digital Services, AT&T Technical
Reference 62415, June 1989
4.
AT&T Private Line Service OC-3 Interface Specification, AT&T Technical Reference 54018,
November 1991
5.
AT&T Private Line Service OC-12 Service Description and Interface Specification, AT&T Technical
Reference 54077, July 1998
6.
ANSI T1.101-1994, “Synchronization Interface Standards,” 1994
7.
ANSI T1.105.01-1995 “Telecommunications – Synchronous Optical Network (SONET) – Automatic
Protection Switching,” 1995
8.
ANSI T1.105.02-1995“Telecommunications – Synchronous Optical Network (SONET) – Payload
Mappings,” 1995
9.
ANSI T1.105.03-1995 “Telecommunications – Synchronous Optical Network (SONET) – Jitter at
Network Interfaces,” 1995
10. ANSI T1.105.03a-1995 “Telecommunications – Synchronous Optical Network (SONET) – Jitter at
Network Interfaces – DS1 Supplement,” 1995
11. ANSI T1.105.03b-1997 “Telecommunications – Synchronous Optical Communication (SONET) –
Jitter at Network Interfaces – DS3 Wander Supplement,” 1997
12. ANSI T1.105.04-1995 “Telecommunications – Synchronous Optical Network (SONET) – Data
Communication Channel Protocols and Architectures,” 1995
13. ANSI T1.105.06-1996 “Telecommunications – Synchronous Optical Network (SONET) – Physical
Layer Specifications,” 1996
14. ANSI T1.105.09-1996 “Telecommunications – Synchronous Optical Network (SONET) – Timing
and Synchronization,” 1996
15. ANSI T1.107-1997 “Telecommunications - Digital Hierarchy - Formats Specifications,” 1997
16. ANSI T1.231-1997, “Digital Hierarchy – Layer 1 In-Service Digital Transmission Performance
Monitoring”, 1997
17. ANSI T1.514-1995 “Network Performance Parameters and Objectives for Dedicated Digital Services
– SONET Bit Rates,” 1995
18. Bellcore GR-253-CORECORE, Issue 2 Version 1, “Synchronous Optical Network (SONET)
Transport Systems: Common Generic Criteria”, December 1997
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15
19. Bellcore GR-499-CORE “Transport
Requirements,” Issue 1, December 1995
Systems
Generic
Requirements
(TSGR):
Common
20. Bellcore GR-1244-CORE “Clocks for the Synchronized Network: Common Generic Criteria,” June
1995
21. Bellcore GR-1365 CORE, “SONET Private Line Service Interface Generic Criteria for End Users,”
Issue 1, December 1994
22. ATM Forum af-phy-0046.000 “2488.32 Mbps Physical Layer Specification,” January 1996
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